1. Field of the Invention
The invention relates to an injection molding machine with a vertically displaceable closing unit.
2. The Prior Art
Over the past decades, it has been found that it is useful in the manufacture of articles made of plastic or rubber mixtures to employ injection molding machines with a vertically displaceable closing unit, so that after the molding tool has been opened, the produced articles will project from the horizontal plane of separation of the tool and can thus be removed from the top. This is advantageous when a multitude of mold clusters for relatively small articles is contained in a molding tool. Because of the shape of such articles, which may comprise undercuts, or because of their material, such articles may occasionally pose problems when they are removed from the clusters of the mold, so that they have to be constantly observed by a member of the operating personnel and, if necessary, then have to be removed by hand with or without the use of special tools, or if the injection molding machine is a component of a production line, along which the manufactured articles are transferred to the next treatment station.
In the simplest case, this is carried out in the form of a displacement or swiveling movement in a horizontal plane extending parallel with the plane of separation of the molding tool, in combination with a lifting movement first and a final depositing movement. Since injection molding machines with vertically displaceable closing units generally require a smaller set-up area than corresponding injection molding machines with a horizontally displaceable closing unit, they can therefore be installed in a more flexible way in an existing production plant building.
Furthermore, with injection molding machines comprising a vertically displaceable closing unit, it is useful if the upper cross head (or yoke) is provided in the form of a stationary mold clamping plate, and to support the displaceable mold clamping plate on the lower yoke, which is designed in the form of the counterpressure plate. The displaceable mold clamping plate is displaced against the stationary mold clamping plate. This offers the advantage that the upper cross head (or yoke) will not have to support the driving units for lifting and lowering the displaceable mold clamping plate, which are driving cylinders and additional devices normally present for generating the closing pressure, so that both the struts and the upper yoke can be constructed less massive in a manner saving material.
However, in such a case, the lower yoke must accommodate stops for the driving cylinders and additional devices for generating the closing pressure. However, it does not require any additional reinforcements for increasing the stability, because it is capable of passing on the stresses caused by the driving cylinders and the generation of the closing pressure directly into the underground. In such a case, the required plasticizing and injection unit is mounted either on or above the stationary mold clamping plate so that it feeds the flowable plastic melt or a flowable rubber mixture into the sprue from the top, which vertically extends in the stationary mold clamping plate, or into some other suitable type of system, or it is driven laterally against the plane of separation of the molding tool in order to inject the flowable plastic melt or a flowable rubber mixture from the side into a system of distribution channels arranged in the plane of separation.
One or more hydraulically actuated driving cylinders with a small cross section and great stroke length are usually employed as driving units for injection molding machines of the type specified above, for lifting and lowering the displaceable mold clamping plate. The ends of the cylinder housings of such driving cylinders facing away from the displaceable mold clamping plate are stopped in or on the marginal zone of the counterpressure plate, and the ends of their piston rods facing away from the counterpressure plate are secured on the displaceable mold clamping plate in a form-locked manner in or on the marginal zone of the plate. In the present case, the closing pressure is then generated by a pressure cushion arranged in the counterpressure plate. According to the state of the art, such a pressure cushion consists of a short-stroke cylinder to which hydraulic fluid is admitted on both sides. This cylinder has a larger cross section and a vertical direction of movement with a maximum deflection in the order of magnitude of hk=50 mm. The piston rod of this cylinder has a horizontal end surface in the form of an attachment which, in the idle position of the pressure cushion, is substantially aligned with the upper area of limitation defining the counterpressure plate.
The pressure cushion specified above is usually temporarily coupled to the displaceable mold clamping plate for producing the closing pressure of the molding tool united by the driving cylinders, by a system having a punch with a predetermined length and adequate stability and connected in a force-locked manner with the underside of the displaceable mold clamping plate and pointing downwards from there. With the displaceable mold clamping plate positioned in the lowered position, the punch immerses in a central bore of the piston and the attachment-like piston rod of the pressure cushion, which forms a ring piston, as well as in a bore in the underside of the counterpressure plate, and, with the displaceable mold clamping plate located in the lifted position, comes to a standstill with its lower horizontal end surface just barely spaced on top from the upper—now ring-shaped—end surface of the attachment-like piston rod. The spacing is such that an adequately stable swinging disk can be folded from the side into the gap between the lower surface of the punch and the upper end surface of the piston rod; or coupled by means of a pressure block, i.e. a punch having a predetermined length and adequate stability as well, which, with the displaceable mold clamping plate in the extended condition, can be swiveled from the side between the underside of the displaceable mold clamping plate and the upper end surface of the attachment-like piston rod of the short-stroke cylinder.
The first-mentioned type of coupling is realized, in machines that employ a punch that has not only a preset length but a constant length as well. If it is desired to adapt the injection molding machine to different molding tool levels in the stationary mold clamping plate, the machine comprises a mechanical type of vertical adjustment that is integrated in the molding clamping plate and effective vis-a-vis the upper ends of the struts. This level adjustment, however, leaves the force-locked connection between the clamping plate and the struts untouched in whichever condition it has been fixed. The second-mentioned type of coupling is employed, for example in molding machines manufactured by the Dieffenbacher Company. However, this type of coupling has been a component already in revolving table-type injection molding equipment employed in the eighties for producing articles from rubber mixtures manufactured by Klöckner Ferromatik Desma GmbH. With the injection molding machines of the Dieffenbacher Company, the machine is adapted to different molding tool levels by mechanically extending or shortening the pressure block by means of a thread that is arranged integrated in the block.
In connection with all injection molding machines of the type described above, however, it was found that due to the integration of the pressure cushion in the counterpressure plate, the total height comprising the counterpressure plate and the lowered displaceable mold clamping plate including the half of the molding tool clamped on the latter, and thus the level at which the molding machine is controlled must not fall short of a preset minimum value in the order of magnitude of hB=1000 mm. This means that the plane of separation of the lowered half of the molding tool and of the produced injection-molded articles projecting from this half of the tool can be ergonomically handled only if the machine is installed in a costly pit, or the person in charge of controlling the machine is required to work standing on a small podium, which is accident-prone because the operator is required to frequently step down from and up again on the podium.